October 1, 1887.] 



♦ KNO^A^I.EDGE ♦ 



279 



unsteady as to preclude the possibility of work, except with 

 the utmost difficulty. To obviate any such mishaps the 

 author has devised a dish, shown in section at fig. 1. It 

 may be oval or oblong (preferably the latter) in shape ; its 



Fig. 1. — DissECTiNC Dish. 

 0. Cover ; d. bocly of dish ; j). bed of paraffin. {SrcHoiial Biaijram.) 



sides slope upwards and inwards, and thus effectually 

 prevent tlie bed of paraffin from shifting or floating during 

 the di.ssection. The upper rim of the disli should be 

 indented, so as to admit of a cover which will not easily slip 

 off. Both dish and cover may be made of earthenware, of 

 indurated wood, or the new paper-bottle material invented 

 by Mr. H. L. Thomas, of Chicago, and now being intro- 

 duced into this country by Messrs. Tulk & Co., of Walbrook. 

 Museum Bottles. — One of the gi-eatest difficulties expe- 

 rienced by museum curators has hitherto been in the 

 display, to the fullest advantage; of preparations in spirit. 

 However carefully these are put up, the time arrives, 

 sooner or later, when it is found neces.^ary to readjust the 

 object or to renew the spirit, either on account of evaporative 

 deterioration or discoloration of the fluid. The bottles 

 are necessarily expensive, and those of large sizes usually 

 have to be made specially to order — of such, those with 



Fig. 2.— Patent LoCK-.STurrEE, suitable for Museum Bottles. 



evenly ground tops, over which are fastened circular discs of 

 glass, by means of a more or less spirit-proof, colourless 

 cement, are mostly in vogue, and there certainly is an 

 advantage in the clear transparent top, which admits light, 

 and thus shows every part of the structure displayed to the 

 best advantage ; yet the drawbacks are considerable, e.g., 

 the cases in which they are placed may, and often do, 

 overshadow the transparent tops, which are. moreover, 

 liable at all times to become detached, or, on the con- 

 trary, are found inseparably fastened, when it is ex- 

 tremely desirable to gain access to the preparation. 

 All these objections hive been overcome by the inven- 

 tion of the " Patent Look-Stopper," now being manu- 

 factured on an extensive scale by a Limited Company, 

 whose headquarters are at 57 Moorgate Street, London, E.G. 

 The stopper has never yet been applied to the purpose above 

 mentioned, but is chiefly used for chemicals, pickles, pre- 

 serves, condiments, ikc. It consists of a metallic cap, upon 



the upper surface of which (see fig. 2) there are two nearly 

 semi-circumferential inclined ridges. A. metallic bar, with 

 downwardly projecting catches, which slide into the grooved 

 neck of the bottle, is fastened to the centre of the upper surface 

 of the stopper by a pin or axis, upon which it can rotate 

 horizontally ; so that when the stopper is made to slide 

 side- wise upon the neck of the bottle, and the bar is turned 

 round so as to pass up the ridges, on the edges of the 

 upper surface, as shown in fig. 2, the stopper becomes very 

 firmly attached to the bottle. The under surface is pro- 

 vided with a yielding pad of material which is spii-it, acid, 

 and oil-proof, and when properly adjusted makes a perfectly 

 air-tight; joint. To remove the stopper at any time, bold 

 the bar as shown in the engraving, turn it down the incline, 

 and slide the stopper off; to replaca it, hold the bar, as in 

 the figure, slip both ends into the groove round the neck 

 of the bottle, slide the stopper into its place, and screw the 

 bar up tightly. Specially-made bottles of any size can be 

 provided with stoppers such as that de.scribed above, at 

 a cost not much in excess of that charged for common 

 corks. 



The next contribution will conclude the subject of labo- 

 ratory requisites, and pass on to a consideration of instru- 

 ments and their uses. 



VARYING ASPECTS OF THE EARTH'S 

 GLOBE. 



T is often convenient in astronomical study to 

 consider the apparent aspects of the latitudo- 

 jiarallels and meridians of a globe such as 

 PeP'e' (fig. 1), rotating about an axis aO((', to 

 whicli the polar axis, POP', is inclined. Sup- 

 pose the rotation such as (at the commence- 

 ment of rotation) to bring P towanls the 

 observer, from its position as shown on the edge of the 

 globe — the observer's distance being supposed very great 

 compared with the dimensions of the globe. 



Let us first consider certain properties which will aid 

 in the consideration of these effects, and then exhibit an 

 illustration of the method of construction by which the 

 meridians and parallels of the globe after any given rotation 

 around aOa' m.ay be laid down. 



First, every point on the ylobe PeP'e' or within it de- 

 scribes in reality a circle around the axis aOa', in a plane at 

 right angles to that axis. Seen, therefore, from a distant 

 point of view so placed that the line of sight to is at 

 right angles to the circle P eP'e', any point on or within the 

 globe (supposed for the moment to be transparent) will 

 appear to travel backwards and forwards in a line parallel 

 to t O t', moving from right to left in the nearer half of its 

 course, and from left to right in the farther part. 



Secondly, the rate at which such a point would appear to 

 move in difl'erent parts of its line is very easily deter- 

 mined. Take, as an instance, the point P, and draw 

 Pojj at right angles to a«'. Then the line Pop is that 

 along which the point P would appear to move back- 

 wards and forwards. But we know that in reality the 

 point P is describing a circle, of which P o p is the projected 

 view. Suppose this circle opened out by being rotated 

 about the diameter Pp — into the cucle PRpR'. Then, if 

 the i)oints 1, 2, 3, i, 5, 6, 7, 8, 9, 10, 11, 12 are equi- 

 distant points around the circumference of PRpR', it is 

 quite clear that the uniform rotation around aOa' will 

 bring the point P to the apparent position, q, r, o, s, u, p, 

 u, s, o, r, q, P (obtained by drawing the lines 1 — 11, 2 — 10, 

 3 — 9, ifec), after successive equal intervals of time. We 



